request.getRequestURL() 返回全路径
request.getRequestURI() 返回除去host(域名或者ip)部分的路径
request.getContextPath() 返回工程名部分,如果工程映射为/,此处返回则为空
request.getServletPath() 返回除去host和工程名部分的路径
request.getRequestURL() http://localhost:8080/district_number/html/dataProcess.html
request.getRequestURI() /district_number/html/dataProcess.html
request.getContextPath()/district_number
request.getServletPath()html/dataProcess.html